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Mesoscale Discussion 1130
NWS Storm Prediction Center Norman OK
0324 PM CDT Sun Jun 12 2022

Areas affected...Northeastern Wyoming southeastern Montana and
western South Dakota

Concerning...Severe potential...Watch likely 

Valid 122024Z - 122200Z

Probability of Watch Issuance...80 percent

SUMMARY...Strong to severe storms, should develop this afternoon
from the higher terrain near a quasi-stationary front. Evolving
supercell structures will likely pose a risk for large to very large
hail, strong damaging winds and perhaps a couple tornadoes. A
weather watch is likely before 21z.

DISCUSSION...Mid afternoon water vapor imagery showed an anomalously
deep mid-level trough moving onshore across the Pacific Northwest
and spreading eastward across the central Rockies. Height falls
ahead of this feature are evident in the broad clouds/stratiform
precipitation ongoing across eastern ID and western MT/WY roughly
marking the position of an east-west oriented quasi stationary
front. Over the last half hour lightning has emerged along the front
across northern WY likely in response to strong diurnal heating and
subsequent surface destabilization. As ascent from the approaching
mid-level trough, weak upslope forcing, and surface
heating/moistening along the front continue, remaining MLCINH should
dissipate, resulting in vigorous thunderstorm development across
southern MT and northern WY. 1500 J/kg of MLCAPE and 50+ kt of
effective shear evident on VAD VWPs and the 19z UNR special sounding
suggests supercells will be the dominate storm mode. Strong vertical
shear and the degree of buoyancy/lapse rates suggest large to very
large hail is possible along with damaging wind gusts. Already
backed surface winds hint that low-level hodographs will likely
enlarge through this evening in response to increasing ascent and
strong east/northeasterly upslope flow. The large 0-2km storm
relative winds and enhanced vorticity ingestion along the front
suggest a few tornadoes will also be possible with the more discrete
supercells able to develop. A weather watch is likely needed by 21z
across portions of MT, SD and WY.

..Lyons/Guyer.. 06/12/2022

...Please see www.spc.noaa.gov for graphic product...

ATTN...WFO...BIS...UNR...BYZ...RIW...

LAT...LON   45040785 45660662 45950499 45960377 45740298 45450250
            45050236 44740238 44280279 44060336 43850412 43800501
            43760570 43840650 43970720 44210782 44550811 45040785